This invention relates generally to turbines and more particularly to diaphragm assemblies used with steam turbines.
At least some known steam turbines include diaphragm assemblies that channel flow downstream to rotating turbine blades. Known diaphragm assemblies are stationary and include a plurality of circumferentially spaced partitions. Each partition extends generally radially between an outer band and an inner band. At least some known bands are formed with openings that extend through the band. A cross-sectional shape of the opening is substantially similar to a cross-sectional profile of the partitions.
During assembly of the diaphragm assembly, each partition is aligned with a respective band opening and the partitions are then inserted through the opening such that the partitions are retained in position between the bands. However, because known turbines and diaphragms use advanced aero-shaped partitions, such as bowed partitions, inserting the partitions through the openings may be a difficult task. Specifically, the bowed cross-sectional shape of the partitions may make it difficult to align the partitions with the openings. Such alignment problems, known as fit-up issues, generally increase as the amount of the bow increases and/or as a thickness of a band increases.
To facilitate reducing fit-up issues, at least some known turbines use “booted partitions” to reduce the likelihood of interference between the bands and partitions during assembly. More specifically, within such turbines, the overall size of the openings formed in at least one band are increased such that a clearance gap is defined between the partitions and the bands. A boot is coupled around the partitions to close the gap. However, the booted partitions cause a radial step to be defined at the interface between the boot and the band. The radial steps create flow disturbances reducing the overall stage efficiency and generally such partitions require a larger signature footprint within the turbine.